2^3 x 81 : 3^2 = 8 x 81 : 9
= 8 x 9 = 72
21 + 369 + 79 = ( 21 + 79 ) + 369
= 100 + 369 = 469
16 x 54 + 16 x 46 = 16 x ( 54 + 46 )
= 16 x 100 = 1 600
21 x [ ( 1 245 + 987 ) : 2^3 - 15 x 12 ] + 21 = 21 x [ 2232 : 8 - 180 ] + 21
= 21 x [ 279 - 180 ] + 21
= 21 x 99 + 21 x 1
= 21 x ( 99 + 1 )
= 21 x 100 = 2 100